<script>
  setTimeout(function () {
    console.log(1)
  }, 0);

  new Promise(function executor(resolve) {
    console.log(2);
    for (var i = 0; i < 10000; i++) {
      i == 9999 && resolve();
    }
    console.log(3);
  }).then(function () {
    // 微
    console.log(4);
  });
  console.log(5);
</script>